JPH0919968A - Method for producing polystyrene-based resin foam sheet - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a polystyrene-based resin foamed sheet, which is capable of improving the moldability of a polystyrene-based resin foamed sheet and forming an excellent molded product having no sink mark or the like. According to the method of the present invention, the surface of the polystyrene-based resin extruded foam sheet 1 is brought into contact with a heating roll 2 having a surface temperature of less than 150 ° C. for 0.4 seconds or more to heat the surface of the foam sheet 1 to anneal it. This is a method for obtaining a polystyrene resin foam sheet with improved moldability. In the method of the present invention, the surface temperature of the heating roll 2 is 145 ° C.
It is preferable that the Vicat softening point of the base resin of the polystyrene-based resin foam sheet 1 is not less than + 10 ° C. The heating roll 2 is preferably one whose surface is coated with a polytetrafluoroethylene resin.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polystyrene resin foam sheet.

[0002]

2. Description of the Related Art A polystyrene-based resin foam sheet obtained by melt-kneading a polystyrene-based resin with a foaming agent in an extruder and then extruding and foaming from the extruder is used for obtaining a molded product such as a food container by thermoforming. Widely used as a forming sheet. By the way, the polystyrene-based resin foamed sheet may cause molding defects such as cracks in the obtained molded product due to poor elongation during thermoforming.

In order to improve the moldability of such a polystyrene-based resin foamed sheet, a method has been proposed in which the surface of the foamed sheet is subjected to a heat treatment (such heat treatment is sometimes referred to as annealing). For example, Japanese Patent Fairness 5-3
No. 820, the extruded foamed sheet of polystyrene resin is passed between a heating roll and a pressure roll, and is heated at a temperature of 150 to 250 ° C. for one hour by the heating roll to improve the formability of the foamed sheet. In addition to the above, a method has been proposed in which the surface of the foamed sheet can be made whiter to improve the appearance. In this method, the foamed sheet is momentarily brought into line contact with the surface of the heating roll to heat the foamed sheet in a short time.

[0004]

However, in the method described in Japanese Patent Publication No. 5-3820, since the polystyrene resin foam sheet is brought into contact with a heating roll having a high temperature of 150 ° C. or higher, the bubbles on the sheet surface burst ( Defoaming) occurs, or the surface becomes keloid-like (the rough surface of the sheet is collectively referred to as “burning” below), and as a result, the appearance of the foamed sheet is deteriorated and heat is generated. There has been a problem that the secondary foaming force required for molding is reduced in a short period of time. Even a foamed sheet having such “burning” can be tentatively thermoformed as long as the secondary foaming force is maintained to some extent. However, when molding a foam sheet with "burn", there is a problem that "burn" becomes more severe when the heating temperature range is not set to an extremely narrow range when heating the foam sheet prior to thermoforming. It was It was also very difficult to control and heat within such an extremely narrow temperature range.

Further, although the polystyrene resin foam sheet generally has unevenness in thickness, the above Japanese Patent Publication No. 5-382.
In the method of heating by contacting with a heating roll instantaneously as described in No. 0, in the case of a foamed sheet having uneven thickness, it is difficult to uniformly contact the heating roll with the sheet surface, and thus the entire sheet surface is Is unevenly heated, which results in
The appearance and thermoformability of the foamed sheet could not be improved uniformly. Also, by increasing the sandwiching force of the sheet between the heating roll and the sandwiching roll so that the heating roll is brought into uniform contact with the surface of the foamed sheet, wrinkles occur on the surface of the foamed sheet, which deteriorates the appearance and bursts of bubbles. Occurs, and the secondary foaming force required for thermoforming is reduced in a short period of time.

The present inventors have conducted extensive studies to solve the above problems, and as a result, heat-treat an extruded foamed sheet of polystyrene resin by contacting it with a heating roll at a temperature lower than that of the conventional method for a longer time than that of the conventional method. As a result, they have found that the drawbacks of the above conventional methods can be solved, and have completed the present invention.

[0007]

That is, the method for producing a polystyrene-based resin foamed sheet of the present invention comprises contacting the surface of a polystyrene-based resin extruded foamed sheet with a heating roll having a surface temperature of less than 150 ° C. for 0.4 seconds or more. It is characterized by heating. In the method of the present invention, the surface temperature of the heating roll is 1
It is preferable that the temperature is 45 ° C. or lower and the Vicat softening point of the base resin of the polystyrene resin foam sheet is + 10 ° C. or higher. The heating roll is preferably one whose surface is coated with a polytetrafluoroethylene resin.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polystyrene resin foam sheet used in the present invention is an extruded foam sheet obtained by melt-kneading a polystyrene resin and a foaming agent in an extruder and then extruding from the extruder to foam. The foamed sheet foamed by the extruder is usually wound into a roll and then treated in a step different from the foaming step by bringing it into contact with a heating roll while unrolling from the roll body (offline). Treatment), a method in which a sheet extruded and foamed from an extruder is processed by bringing it into contact with a heating roll before being wound into a roll, and then wound into a roll (online processing)
May be adopted. As the polystyrene resin, styrene homopolymer, p-methylstyrene homopolymer, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer. , A styrene-butadiene copolymer, a styrene-butadiene-acrylonitrile copolymer, a mixture of polystyrene and polyphenylene oxide, and the like. The MFR of the styrene resin is not particularly limited, but it is preferably about 0.1 to 60 g / 10 minutes.

As the foaming agent, a volatile foaming agent, an inorganic gas type foaming agent, a decomposition type foaming agent and the like are used. Examples of volatile foaming agents include propane, butane, pentane, hexane and other aliphatic hydrocarbons, cyclobutane, cyclopentane and other cycloaliphatic hydrocarbons, trichlorofluoromethane, dichlorodifluoromethane, 1,2-dichloro -1,1,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1,1-dichloro-2,2,2-trifluoroethane,
Examples thereof include halogenated hydrocarbons such as methyl chloride, ethyl chloride and methylene chloride. Examples of the inorganic gas-based foaming agent include inert gases such as carbon dioxide, nitrogen and air. Examples of the decomposition-type foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutylnitrile, sodium bicarbonate and the like. Two or more kinds of these foaming agents can be mixed and used.

In the method of the present invention, the polystyrene resin foamed sheet is heated by contacting the surface of the heating roll for 0.4 seconds or more. The heating roll used for heating the foamed sheet has a surface temperature of less than 150 ° C. is necessary. When the foamed sheet is brought into contact with a heating roll having a surface temperature of more than 150 ° C. and heated, the sheet is apt to be “burned”. In the method of the present invention, the surface temperature of the heating roll is preferably 145 ° C. or lower from the viewpoint of safety in preventing “burn”, and the Vicat softening of the base resin of the polystyrene resin foam sheet from the viewpoint of heat treatment efficiency of the foam sheet surface. The temperature is preferably + 10 ° C. or higher.

On the other hand, if the contact time between the foamed sheet and the heating roll is less than 0.4 seconds, the elongation of the sheet when the sheet is thermoformed becomes poor, and a so-called "naki" occurs during the forming.
May easily occur, or the molded product may be easily cracked by impact. The contact time between the foamed sheet and the heating roll is preferably 0.5 to 10 seconds. The foamed sheet obtained by the method of the present invention has good slip on the heat-treated surface, and molded articles such as containers obtained by molding this foamed sheet also have good slippage, but the contact between the heating roll and the foamed sheet If the time is less than 0.4 seconds, the sheet will have insufficient slipperiness. If the slipperiness of the molded product such as the container is good, when taking out the molded containers and the like one by one from the stacked state, there will be no trouble such as two or more overlapping and taking out. Further, in automatic filling packaging in which the container is conveyed while repeating movement and stop of the container and the product is sequentially filled in the container during the conveying step, a step of stopping the container transfer while the container is slid on the conveying means. However, the container obtained by molding the foamed sheet obtained by the method of the present invention so that the heat-treated surface is located on the outside has a good sliding property on the bottom surface of the container, and therefore the container is slid to stop the transfer. Even in the closed state, there is little risk that the containers will overlap with each other or fall over.

In order to bring the polystyrene resin foam sheet and the heating roll into contact with each other, as shown in FIG.
Is wound around the surface of the heating roll 2 to bring the sheet 1 into surface contact with the heating roll 2. Foam sheet 1
The contact time between the heating roll 2 and the heating roll 2 can be adjusted by changing the rotation speed of the heating roll 2 and the contact length between the foam sheet 1 and the heating roll 2. The contact length between the foamed sheet 1 and the heating roll 2 is adjusted by the line segment connecting the point A where the foamed sheet 1 starts contact with the heating roll 2 and the center of the heating roll 2, and the foamed sheet 1 by the heating roll 2. The angle formed by the line segment connecting the point B away from the center of the heating roll 2 and:
It is performed by adjusting θ (hereinafter, this angle is referred to as a holding angle). The set value of the holding angle varies depending on the diameter of the heating roll 2 and the difference in the rotation speed of the heating roll 2. Generally, the rotation speed of the heating roll 2 (peripheral speed of the roll surface) is 3 to 30.
If the heating roll has a diameter of 200 mm, the holding angle θ is 20 to 180 °, and the diameter is 300 mm.
In the heating roll of No. 3, the holding angle: θ is 15 to 120 °, and in the heating roll having a diameter of 400 mm, the holding angle: θ is 10 to 9
It is about 0 °.

The wrapping angle: θ can be adjusted, for example, by providing two tension rolls 3a and 3b with the heating roll 2 interposed therebetween and moving the tension rolls 3a and 3b up and down. In the case shown in FIG. 1, by moving the tension rolls 3a and 3b upward,
The included angle θ between the foam sheet 1 and the heating roll 2 becomes small, and as a result, the contact length between the foam sheet 1 and the heating roll 2 decreases. On the contrary, when the tension rolls 3a and 3b are moved downward, the included angle θ between the foam sheet 1 and the heating roll 2 becomes large, and as a result, the contact length between the foam sheet 1 and the heating roll 2 increases.

The contact time between the foamed sheet 1 and the heating roll 2 is not limited to the adjustment of the wrapping angle: θ, but as shown in FIG.
It is also possible to adjust by providing the above heating rolls 2a and 2b and sequentially bringing the foamed sheet 1 into contact with the surfaces of these heating rolls 2a and 2b. In FIG. 2, 3a, 3b, and 3c indicate tension rolls.

The effect of the heat treatment of the foamed sheet 1 by the method of the present invention is more effective when the foamed sheet 1 is heated by the heating roll 2 and the method of applying pressure between the pinching roll 4 and the heating roll 2 is used in combination. When the foamed sheet is pressed between the pinching roll 4 and the heating roll 2, during the heating process of the foamed sheet 1 by the heating roll 2 (especially, 0.
It is preferable to provide the pinching roll 4 so that the pinching roll 4 comes into contact with and presses the foamed sheet 1 after one second or more has elapsed). When the step of pressurizing the foamed sheet 1 with the pressing roll 4 and the heating roll 2 is provided, as shown in FIG. 3, the foaming sheet 1 is contacted so as to be wound around the heating roll 2 and the pressing roll 4 alternately so as to foam. The sheet 1 may be heated by the heating roll 2 and then pressed by the pinching roll 4 and the heating roll 2. The pressing force (linear pressure) applied to the foam sheet 1 by the heating roll 2 and the pinching roll 4 is 3.0.
It is preferably 10 kg / cm. The pinching roll 4 does not normally have a heating mechanism.

When the foaming sheet 1 is pressed by the pressing roll 4, the pressing pressure is applied before the foaming sheet 1 is heated to some extent, such as immediately after the heating of the foaming sheet 1 (before 0.1 seconds has elapsed from the start of heating). When the foamed sheet 1 is pressed by the roll 4 and the heating roll 2, bubbles in the foamed sheet 1 may burst. As shown in FIG. 1, the foam sheet 1
At the point A where the contact with the heating roll 2 starts and the foam sheet 1
When the pressing roller 4 is provided so that the pressing roller 4 contacts the foamed sheet 1 at a point approximately midway from the point B where the sheet is separated from the heating roller 2, the foamed sheet 1 is pressed.
Is preferable because even tension is applied before and after the heating roll 2.

Not only one side of the foamed sheet 1 is heated, but also one side of the foamed sheet 1 is brought into contact with the heating roll 2a as shown in FIG. 4, and then the other side of the foamed sheet 1 is heated to the heating roll 2b. Both sides of the sheet 1 may be heated by bringing them into contact with each other. In FIG. 4, 4a and 4b
Indicates a clamping roll, and 3a, 3b, 3c and 3d indicate tension rolls.

In the method of the present invention, as described above, the surface temperature of the heating roll 2 is lower than 150 ° C., which is lower than that of the conventional method, but the foamed sheet 1 is in contact with the heating roll for a longer time than the conventional method. Therefore, the foamed sheet 1 is easily fused to the heating roll 2. Therefore, it is preferable that the heating roll 2 has a surface coated with a polytetrafluoroethylene resin.

In the method of the present invention, a polystyrene resin film may be laminated on the foamed sheet 1 which is brought into contact with the heating roll 2 and subjected to heat treatment, if necessary.
In the example shown in FIG. 1, while extruding the polystyrene-based resin film 5 from the extruder 6, a method of laminating the polystyrene-based resin film 5 on the non-heat-treated surface of the foamed sheet 1a between the pressure rolls 7a and 7b (extrusion laminating method). ) Is shown. The polystyrene-based resin film and the foamed sheet are not limited to the case where they are laminated by the extrusion laminating method as shown in FIG. 1, but a polystyrene-based resin film produced in a separate step in advance is heat-sealed with the foamed sheet to form a heat-laminating method. You may laminate by.

As the base resin of the polystyrene resin film, the same polystyrene resin as the base resin of the foam sheet 1 can be used. The polystyrene resin film may be laminated on the surface of the foamed sheet 1 on which the heat treatment has been performed or may be laminated on the surface of the foamed sheet 1 on which the heat treatment has not been performed.
The foamed sheet 1 may be laminated on only one side or both sides. Specific examples of the laminated sheet obtained by laminating the polystyrene resin films include those of the following embodiments. In addition, as a laminating method at this time, an extrusion laminating method or a thermal laminating method (a method of laminating the foamed sheet and the film by heating the film-side roll when passing between the rolls) Is common.

A product in which a polystyrene resin film is laminated only on the heat-treated surface of the foamed sheet 1 having only one surface heat-treated. A product in which a polystyrene-based resin film is laminated only on the non-heat-treated side of the foam sheet 1 whose one side is heat-treated. A product in which a polystyrene-based resin film is laminated on both sides of a foamed sheet 1 whose one side is heat-treated. A product in which a polystyrene resin film is laminated only on one side of a foamed sheet 1 whose both sides are heat-treated. A product in which a polystyrene resin film is laminated on both sides of a foamed sheet 1 whose both sides are heat-treated.

The polystyrene resin film is laminated on only one side of the foamed sheet 1, laminated on both sides, or the polystyrene resin film is laminated on the heat-treated surface of the foamed sheet 1 or laminated on the non-heat-treated surface. Whether to do is appropriately selected according to the purpose of use of the laminated sheet, but when a polystyrene resin film is laminated on the heat-treated surface of the foamed sheet 1 by a thermal lamination method,
Such a laminated sheet is particularly suitable for thermoforming applications because it has excellent adhesive strength and the advantage that the film does not easily peel off.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. Example 1, Comparative Examples 1 and ² A roll body obtained by extruding a foamed extruded sheet (width 1040 mm) having a thickness of 2.3 mm and a basis weight of 250 g / m ² and using polystyrene having a Vicat softening point of 105 ° C. as a base resin. While sequentially feeding out the foamed sheet, the foamed sheet is brought into contact with the heating roll (diameter 200 mm) according to the method shown in FIG. 1, and the foamed sheet is approximately at the midpoint of the portion where the foamed sheet is in contact with the heating roll. Was pressed by a pinching roll (without a temperature control mechanism). The distance between the heating roll and the pinching roll was 1.3 mm when the foamed sheet was not passing, and was 1.8 mm when the foamed sheet was passing. The thickness of the foamed sheet after being heated and pressed was 2.3 to 2.4 mm.

Next, a high impact polystyrene (HIPS) film (film basis weight 140 g /
m ² ) was laminated and then wound again into a roll shape. Surface temperature of the heating roll, rotation speed of the peripheral surface of the heating roll, contact length between the foam sheet and the heating roll, contact time and holding angle, clamping pressure (linear pressure) between the pressure roller and the heating roll on the foam sheet Is shown in Table 1. Table 1 also shows the glossiness of the heat-treated surface of the laminated sheet (measured from the longitudinal direction of the laminated sheet) and the occurrence of “burn”. The glossiness of the heat-treated surface was measured by a perfect digital portable gloss meter “PG-3D” manufactured by Nippon Denshoku Industries Co., Ltd. (5 point measurement with an irradiation angle of 60 °). This glossiness was a measure of the degree of annealing of the heat-treated surface, and the glossiness of the foamed sheet that had not been heat-treated was 13.0%.

The laminated sheets were sequentially unrolled from the roll obtained by winding the laminated sheet obtained as described above, and continuous thermoforming of the container was carried out so that the HIPS laminated surface side of the laminated sheet was located on the inner surface side of the container. . In this case, the number of containers taken per shot was 5 in the length direction of the laminated sheet and 5 in the width direction. The container obtained by molding has a length of one side of the opening of about 16 cm (about 17.5 c including the lip portion).
m), which is a rectangular container having a length of one side of the bottom of about 13 cm. Table 1 also shows the state of occurrence of "pimples" on the upper side wall of the container. The occurrence state of "Naki" was shown by the number of containers in which "Naki" was observed by observing 25 containers. When a similar polystyrene foam sheet that was not heat treated was molded, "Naki" was found in 12 out of 25 containers.

[0026]

[Table 1]

[0027]

As described above, according to the method of the present invention, the foamed sheet is heat-treated by bringing the polystyrene resin foamed sheet into contact with a heating roll having a surface temperature of less than 150 ° C. for 0.4 seconds or more. Therefore, unlike the conventional method in which heat treatment is performed with a high-temperature heating roll, “burn” is unlikely to occur on the surface of the foamed sheet. Further, in the method of the present invention, the foamed sheet is heated by bringing it into contact with a heating roll for 0.4 seconds or more, so that the entire surface of the foamed sheet can be uniformly heated even if the foamed sheet has uneven thickness. As a result, according to the method of the present invention, the appearance of the polystyrene resin foam sheet,
In addition to being able to effectively improve the moldability, the effect of improving the appearance and the moldability appears uniformly regardless of the portion of the foamed sheet.

The foamed sheet produced by the method of the present invention is
Good sliding of the heat treated surface. Therefore, molded articles such as containers thermoformed from the foamed sheets produced by the method of the present invention may have a problem that two or more pieces are taken out in overlapping even if they are taken out one by one in use after being stacked and stored. There is no Further, the container formed by molding the foamed sheet produced by the method of the present invention so that the heat-treated surface is on the outer side is a step of sequentially conveying the container, a step of filling the contents such as food into the container on the conveying device, and a conveying device. When applied to automatic filling packaging that includes at least the step of stopping the movement of the container while sliding the container on and / or on the transfer device, the container is slid because the bottom of the container has good slippage. When the movement of the containers is stopped in the closed state, occurrence of troubles such as overturning of the containers and overlapping of the containers is prevented.

Further, for example, a plurality of products such as cup noodles are stored in the same cardboard box for storage, transportation and sale, but the cardboard box is often thrown during transportation or the like. In such a case, if a container formed by molding a polystyrene resin foam sheet is used as the cup noodle container,
Although the container was sometimes damaged by impact, the foamed sheet produced by the method of the present invention and molded products such as a container molded from the foamed sheet have excellent impact resistance, and the container may be damaged even in the above cases. There is no Further, when a polystyrene-based resin film is laminated on the heat-treated surface of the foamed sheet obtained by the method of the present invention, the adhesive strength of the film is improved and there is little risk of peeling of the film.

In the method of the present invention, when the surface temperature of the heating roll is 145 ° C. or lower and the Vicat softening point of the base resin of the foamed sheet is + 10 ° C. or higher, the heat treatment efficiency is kept high. It is possible to prevent the occurrence of burns. Further, in the method of the present invention, since the foamed sheet is brought into contact with the heating roll for 0.4 seconds or more, the surface temperature of the heating roll is 1
If the temperature is lower than 50 ° C., the foamed sheet is likely to be fused to the heating roll even if the temperature is lower than the conventional temperature. Therefore, coating the surface of the heating roll with a polytetrafluoroethylene resin has the effect of effectively preventing fusion of the foamed sheet to the heating roll.

[Brief description of the drawings]

FIG. 1 is a schematic process drawing showing an example of heating one side of a foamed sheet in the manufacturing method of the present invention.

FIG. 2 shows an example of heating using a plurality of heating rolls,
It is a process schematic diagram near a heating roll.

FIG. 3 is a process schematic diagram in the vicinity of a heating roll showing a case where heating by a heating roll is different.

FIG. 4 is a process schematic diagram in the vicinity of a heating roll showing an example of heating both sides of a foamed sheet.

[Explanation of symbols]

 1 Polystyrene resin foam sheet 2 Heating roll

Claims (3)

[Claims] 1. A method for producing a polystyrene-based resin foamed sheet, which comprises heating the surface of an extruded polystyrene-based resin foamed sheet to a heating roll having a surface temperature of less than 150 ° C. for 0.4 seconds or more. 2. The method for producing a polystyrene resin foam sheet according to claim 1, wherein the surface temperature of the heating roll is 145 ° C. or lower, and the Vicat softening point of the base resin of the polystyrene resin foam sheet is + 10 ° C. or higher. 3. The method for producing a polystyrene-based resin foam sheet according to claim 1, wherein a heating roll having a surface coated with polytetrafluoroethylene resin is used.